Goliath Fall 2016
Post PDR Redesign
By: Dylan Hong (Design and Manufacturing Engineer)
Approved by Kristen Oduca (Project Manager)
Table of Contents
Introduction
Requirement: Goliath shall be a scale model of the Goliath 302.
Our initial design did not meet our level one requirements of a six hour print time, thus some changes need to be made. The customer wanted to make the Goliath “as humanly small as possible,” where the electronic components are tightly fitted within the Goliath’s body. This smaller form factor forced us to change the scaling of the body and sub-components of the body including the wheels and tracks. Also, this meant we had to resort to smaller motors, sensors, and different placement of our smartphone. Instead of incorporating the smartphone into the Goliath’s body, we decided to have it placed on top of the Goliath. A double sided suction cup will be place on top of Goliath and the Android phone, as shown in Figure 1 and 2.
Figure 1 – Phone on Top of Goliath Angled View
Figure 2- Phone of Top of Goliath Side View
Design Process
Body Dimensions
For our initial design, we based the dimensions of the body from our Samsung Galaxy S6, but for our redesign, we decided to base the dimensions off our 3DOT Board and newly selected motors. The 3DOT Board is roughly around 2.75 x 1.5 x 0.75 inches and the micro gearbox motor is measured approximately at 1.37 x 0.39 x 0.47 inches. With this information, we were able redesign the Goliath to be about 4.27 x 2.09 x 1.5 inches.
In comparison, our initial dimensions of 4.27 x 2.94 x 1.5 inches were very close in approximation with the ideal dimensions of 4.27 x 2.39 x 1.58 inches with a percent error of 0 x 23.01 x 5.06 %. These calculations are shown in Figure 3.
Figure 3 – Percent Error of Goliath
The width of our initial dimensions is larger than the ideal dimensions because we had to compensate with the placement of the micro gearbox motor. The size of the micro gearbox motor inside the Goliath is shown in Figure 4.
Figure 4 – Micro Gearbox inside Goliath
Computer Simulation
3D Model
After figuring out the dimensions of our new design, I was able to 3D model the electronic components within the body of the Goliath. The 3DOT Board, micro gearbox motors, and last semester’s PCB are displayed tightly fitted inside the chassis.
Next, I modeled the Goliath with temporary tracks. The Goliath is modeled with an iPhone 6 and a periscope to mimic what our prototype will look like previously shown in Figure 2. The smartphone will be placed on top of the Goliath with the use of a double-sided suction cup. The suction cup will hold its position only if it is placed on a smooth surface. This resulted in changing the top panel design from an open surface to a closed surface. Also, since the design is in a much smaller form factor, the smaller wheels were changed from road wheels to idle wheels. I will have to perform a trade-off study to see how well idle wheels will work to move the tracks when compared to road wheels. Furthermore, the tracks and larger wheels will no longer be prefabricated since it will be harder to find and purchase small wheels. We will 3D print the wheels and tracks since the small form factor will greatly reduce print time.
The 3D modeling of the micro gearbox motors and temporary tracks were obtained from grabcad.com.
Exploded View
I created an exploded view to show all the components of the Goliath shown in Figure 5.
Figure 5 – Goliath Exploded View
Drawings
I created drawings on Solidworks to represent the different view angles, the parts involved in the chassis, and the electronic components within the chassis of the new design. The drawing provides an outline of the model and displays the labeled parts of the Goliath, shown in Figure 6, 7, and 8.
Figure 6 – Drawing of Goliath from All Angles
Figure 7 – Drawing of Goliath Outside View
Figure 8 – Drawing of Goliath Inside View
Rendering
Rendering generates a life-like image of a 3D mode. We rendered using Photoview 360 to enhance the Goliath at maximum quality with a background image of an environment consisting of snow. This image used for our PDR title page showed in Figure 9.
Figure 9 – Goliath Rendering
Static Study
We performed a static study, which analyzes stress, strain and displacement of force being applied to areas of the model. The static studies are shown in Figure 10, 11, and 12.
Figure 10 – Stress Analysis
Figure 11 – Strain Analysis
Figure 12 – Displacement of Force Analysis
First, we did a back of the envelope calculation of the force applied from our smartphone to the top panel of the Goliath. We weighed the Samsung Galaxy S6, which was 4.87 grams and determined the acceleration of gravity of 9.8 meters per second squared. Force is equated to mass multiplied with acceleration, in which we calculated:
Figure 13 – Force Calculations
Second, we chose the material of our Goliath to be ABS plastic and applied the force of 1.35 N to the top panel, while the bottom wheels and panel were fixed.
Third, we analyzed the stress and strain, which is the change in shape of an object and came to a conclusion that the top panel became slightly bent and deformed at approximately 4.45e+004 von Mises.
Finally, the displacement analysis represents the change in position. The force applied changed the position of the top panel to be concaved. The deformation of the top panel is due to the kind of material used and the lack of support. For future studies, we will add ribs underneath the top panel to garner better support to withstand the force of the phone and to avoid any change in the structure.
Full Scale Prototype
3D Printing
Now that we have new dimensions and 3D modeled the Goliath, I was able to work with my division manager to find out the 3D print time of our model with the use of the Makerbot software shown in Figure 14.
Figure 14 – Model on Makerbot
For our first trial, we used the settings from the initial design, except we set the quality at low quality, while the rest of the settings were the same with a layer height of 0.20mm, 20% infill, raft, and 3 shells. The material we used was PLA with an extruder temperature of 230 degrees Celsius. The total print time was estimated to be about two hours and forty minutes. We were able to meet our level one requirement by a long shot when compared to our initial design. However, this first print did not meet our expectations due to its fragility and low quality, shown in Figure 15.
Figure 15 – PLA with an Extruder Temperature of 230 Degrees Celcius
For our second trial, we decided to use a different printing material known as NGEN co-polymer instead of PLA and changed the print quality to standard. The total print time was estimated to be about four hours and forty-two minutes. This print was successful because it met the level one requirement and it produced a much sturdier quality than the first trial. The only issues that we came across was the extruded holes that were created in Solidworks were too small to fit our 3mm shaft for the drive wheels and that the side panel were too thin. Also, we did not consider fastening methods to connect the parts with ease and had to use tape to put the parts together.
For our future prints, we will increase the thickness of the side panel and combine the side panel and box panel to become one entity to ease fastening issues. We will increase the hole size for the wheels and create a fastening method to connect the panels without tape.
Design and Unique Task
- The chassis parts for the full scale prototype needs to be connected in a functional matter:
- As of now tape is being used to fasten the parts together
- Possible solutions include redesigning the parts to incorporate hinges, snap hook features, micro screws, or 3D printing multiple parts as one entity with each part printing under two hours.
- The subcomponents including the drive wheels, road wheels, and tracks of the Goliath:
- The drive and large road wheels did not have correct hole dimensions, the 3mm steel rod could not fit into the wheels or side panels
- Possible solutions include creating a bigger extruded hole
- Perform tradeoff study for small road wheels vs. small idle wheels
- Tracks are currently nonexistent for this prototype, due to the change in design we could not use prefabricated tracks and could not model our own tracks within the time frame of PDR
- Possible solutions include 3D printing the tracks with flexible printing material and ensure the dimensions of the tracks are correct
- Make sure tracks replicate the tracks of the actual Goliath
- A tradeoff study between smartphones shall be performed due to failures in implementing the Samsung Galaxy S6 with the periscope in regards to producing a live feed for the Biped:
- Smartphones that will be studied are the LG G2, iPhone 6 and Samsung Galaxy S6
- With the height of the Goliath being at around 1.5 inches, the placement of the sensors will play a factor in detecting biped:
- Depending on biped’s dimensions, our current Goliath model will only detict its legs
- Possible solutions include placing the sensors at a certain angle so it can accurately track the Biped
- Work with the electronics and control engineer to obtain PCB schematic in order to assemble and layout the PCB
Conclusion
Overall, our preliminary redesign was successful in terms of our dimensions, 3D modeling, static studies, and prototyping. The small form factor proved to be a difficult challenge because we had to tightly fit each electronic component without sacrificing functionality. However, the small size helped us reach a total print time of four hours with about two hours left for additional prints such as the tracks. The tracks will be modeled and printed for our next prototype and more changes such as fastening methods, and thicker parts will be implemented. The static study helped us figure out the need for support for the top panel when a force of 1.35 N is applied, which we will remodel in the future. As for the prototype, we will use ABS material due to customer request and include further details in order to replicate the actual appearance of the 302 Goliath.